This invention relates to the treatment of sheet material workpieces to reduce the thickness of selected regions thereof. One instance of such treatment is to be found in the manufacture of shoes wherein certain regions, particularly the edges, of shoe upper components are reduced in thickness (or "skived") prior to assembling the shoe upper. Skiving is effective to reduce bulkiness in the upper and to aid its assembly, and thus to improve the appearance of the finished upper and to avoid discomfort of the wearer.
One known method of skiving is described in GB-A-1178960. The method involves supporting a workpiece between an upper and a lower feed roller whilst it is fed to a band knife. Sandwiched between the workpiece and the upper roller is a matrix (hence the method is referred to as "matrix skiving") which carries a relief pattern having raised regions corresponding to the workpiece regions that are subsequently to be reduced by the band knife. The regions of the workpiece engaged by the raised relief pattern are forced downwards against a compressible surface on the lower roller, and consequently below the cutting plane of the band knife. Any portion of the workpiece disposed below the cutting plane is removed by the knife as it is fed therepast, and thus a workpiece is produced with a pattern of reduced thickness regions that match the raised relief pattern of the matrix.
There are, however, problems associated with this existing method of matrix skiving namely that each workpiece and each pattern requires a unique matrix, and the matrix has manually to be registered with the workpiece prior to sandwiching the workpiece and matrix between the feed rollers, which involves time and effort on the part of the operator that can affect output potential. In addition, there is some difficulty involved in achieving successful registration of the workpiece and matrix, and this difficulty enhances the possibility of producing inaccurately skived workpieces.
U.S. Pat. No. 3,538,723 describes an apparatus and method of splitting sheet material workpieces, that is, tanned hides. A support roller has heightwise adjustable sections that enable differing degrees of support pressure to be applied across the width of the hide. The potential variation in support pressure provides the possibility of compensating for the inherent non-uniformity in the thickness of the hide and consequently prevents excessive compression, which could result in the production of a non-uniformly split hide. However, as the process relates to splitting rather than skiving, the hide is supported in a position such that the cutting plane of the knife to which the hide is fed lies at all times within the material of the hide.